This invention is directed to ink and liquid developer compositions, and more specifically to the aforementioned compositions with a polymer core coated with a silica shell onto which reactive dyes have been grafted. In one embodiment, the present invention is directed to heterophase ink jet inks comprised of water, a solvent such as an alkylene glycol, and pigment comprised of a polymer core with a coating thereover of a silica shell, and wherein the shell has grafted thereon reactive dyes. In another embodiment of the present invention there are provided liquid developer compositions comprised of a liquid hydrocarbon medium, a polymeric material soluble in the liquid medum, a charge control agent, and colored particles comprised of a polymeric core with a coating thereover of a silica shell onto which have been chemically grafted reactive dyes. The pigment or pigments selected for the ink jet inks, and liquid developers of the present invention in one embodiment thereof is comprised, for example, of a polymer core, such as poly(methylmethacrylate), with a small effective average particle diameter of from about 0.05 to 4 microns, and preferably from about 0.1 to about 2 microns, and preferably of a density as determined with a Micromeritics Autopycnometer of from about 0.9 gram per cubic centimeter to 1.2 grams per cubic centimeter, which core is coated with an effective thin silica shell of, for example, about 0.002 to about 0.030 micron, and preferably from about 0.005 to about 0.01 micron in thickness, and onto which reactive dyes are grafted to thereby impart color to the ink composition. Also, the present invention is directed to positively charged or negatively charged liquid developers where known charge directors such as barium petroates, Lecithin and the like are selected to permit negatively charged developers, and known charge directing components such as zirconium octoate, iron naphthenate, and a polyisobutylene based polyester are selected to permit positively charged developers. The compositions of the present invention can be selected for the development of images in various imaging processes providing, for example, that the ink jet inks are selected for ink jet printing processes, including the liquid development processes described in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference; xerographic processes, electrographic recording, electrostatic printing, and facsimile systems; color proofing processes; and the process as illustrated in British Patent Publication 2,169,416, published July 9, 1986, and U.S. Pat. No. 4,794,651, the disclosures of which are totally incorporated herein by reference.
Development of electrostatic latent images with liquid developer compositions comprised of, for example, a dispersion of pigments in a liquid hydrocarbon is known. In these methods, the electrostatic latent image, which is usually formulated on a single sheet of photoconductive paper, such as zinc oxide, is transported through a bath of the aforementioned liquid developer. Contact with the liquid developer causes the charged pigment particles present therein to migrate through the liquid to the zinc oxide sheet in the configuration of a charged image. Thereafter, the sheet is withdrawn from the liquid developer bath with the charged pigment particles adhering to the electrostatic latent image in image configuration. The thin film of residual developer remaining on the surface of the sheet is then evaporated within a relatively short time period, usually less than 5 seconds. Also, the marking pigment particles may be fixed to the sheet by heat, for example, in image configuration.
There are disclosed in U.S. Pat. No. 3,554,946 liquid developers for electrophotography comprised of a carrier liquid with a hydrocarbon, negatively electrostatically charged toner particles dispersed in the carrier liquid, and a pigment therein such as carbon black, aniline black, prussian blue, phthalocyanine, blue and cadmium yellow. In accordance with the teachings of this patent, a copolymer is coated on the surface of the pigment particles for the primary purpose of imparting a negative electrostatic charge to these particles. Other patents disclosing liquid developer compositions include U.S. Pat. Nos. 3,623,986; 3,625,897; 3,900,412; 3,976,583; 4,081,391 and 3,900,412. In the '412 patent, there is disclosed a stable developer comprised of a polymer core with a steric barrier attached to the surface of the polymer selected. In column 15 of this patent, there are disclosed colored liquid developers by selecting pigments or dyes, and physically dispersing them by ball milling or high shear mixing. Attempts to obtain useful color liquid developer compositions by the ball milling process described have been, it is believed, substantially ineffective, particularly with respect to obtaining developed images of acceptable optical density in that, for example, the desired size for the latex particles is from 0.2 to 0.3 micron in diameter; and with ball milling techniques, it can be difficult to provide a dispersion of carbon black or other pigment particles much smaller in size than about 0.7 to about 0.8 micron. Consequently, the addition of carbon black pigment particles, for example, to latex particles with a diameter of 0.2 to 0.3 micron while ball milling would result in relatively small latex particles residing on the surface of the pigment particles.
Additionally, there are described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with submicron size marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. There is also illustrated in this patent the use of zirconium octoate as a positive charge control agent with a vinyl resin and Isopar.RTM. Information regarding liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Also of interest are U.S. Pat. No. 3,869,397, the disclosure of which is totally incorporated herein by reference, which discloses the use of zirconium octoate as a negative charge control agent for a carbon black pigment in a vinyl resin, and U.S. Pat. No. 3,939,087, the disclosure of which is totally incorporated herein by reference, which illustrates, for example, a liquid developer comprising a pigment, dye and polymer with zirconium octoate in Isopar.RTM., which octoate can apparently function as a charge director.
In addition, there are illustrated in the aforementioned British Patent Publication 2,169,416 and U.S. Pat. No. 4,794,651 liquid developer compositions comprising toner particles associated with a pigment dispersed in a nonpolar liquid, and wherein the toner particles are formulated with a plurality of fibers or tendrils from a thermoplastic polymer, and carry a charge of polarity opposite to the polarity of the latent image. These toners apparently permit, in some instances, excellent transfer efficiencies, and exhibit excellent copy quality.
Furthermore, there is illustrated in application U.S. Ser. No. 846,164 (now abandoned), entitled Black Liquid Developer Composition, the disclosure of which is totally incorporated herein by reference, stable black submicron liquid developer comprised of an insulating liquid medium having dispersed therein black marking particles comprised of a thermoplastic resin core, which is substantially insoluble in the dispersion medium, and chemically or physically anchored to the resin core an amphipathic block or graft copolymer steric stabilizer, which is soluble in the dispersion medium; and wherein dyes comprised of a specific mixture are imbibed in the thermoplastic resin core with the mixture of dyes being dispersible at the molecular level, and therefore soluble in the thermoplastic resin core and insoluble in the dispersion medium.
Other U.S. patents of interest include U.S. Pat. No. 4,210,805 which discloses toner particles prepared by adding a solvent solution of polyvinylcarbazole to Isopar.RTM. wherein the diameter of the particles is a function of the ratio of solvent to Isopar.RTM., reference column 8; U.S. Pat. No. 4,032,463 which illustrates that the ratio of toluene to Isopar.RTM. effects toner resin particle size; and U.S. Pat. No. 3,766,072 which appears to disclose that resin solvency in the vehicle effects the particle size. Also, in the '463 and '072 patents it is indicated that a solvency increase of the dispersion medium provides a larger final size particle. This occurs, it is believed, because one of the liquids used in formulating such developers is a solvent for the resin that is used. Consequently, the particle will be swollen by the entrapped solvent in the particle yielding a larger particle size. Also, in the polymerization process changing the solvent/nonsolvent ratio of the dispersion medium changes the kinetics and thus the mechanism by which particles are formed. With latex particle polymerization in a hydrocarbon media, usually only submicron size particles are envisioned, reference for example "Dispersion Polymerization in Organic Media", ed. K. E. J. Barrett, Academic Press, 1975. However, it has been shown, reference M. A. Winnik, R. Lukas, W. F. Chen, P. Furlong, and M. D. Croucher, Makromol. Chem., Makromol. Symp. 10/11, 488, (1987), that by varying the solvent/nonsolvent ratio of the dispersion medium for the polymer particle being formed that the particle size may be altered and particles up to 15 microns diameter may be formed. The advantage of this technique for liquid developers has recently been described in U.S. Pat. No. 4,789,616, the disclosure of which is totally incorporated herein by reference.
Although the above described liquid inks are suitable in most instances for their intended purposes, there remains a need for improved inks which can be positively charged enabling their utilization, for example, with layered imaging members which are negatively charged, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. There is also a need for negatively charged inks which can be selected for imaging and printing processes wherein inorganic imaging members including chalcogenides, such as selenium, selenium alloys, doped selenium substances, and doped selenium alloys, including specifically selenium arsenic, selenium tellurium, selenium tellurium arsenic, and the like optionally doped with from, for example, about 200 to about 500 parts of a halogen, such as chlorine, are utilized. Additionally, there is a need for liquid inks containing dyes soluble in the resin binder and insoluble in the carrier component, such as Isopar. Also, there is a need for heterophase ink jet compositions with pigments comprised of a polymeric core coated with a thin silica shell onto which have been grafted dyes and wherein the resulting inks have minimal or substantially no pigment settlement thereby preventing or substantially minimizing undesirable clogging of the ink jets selected for known ink jet printing processes including drop-on-demand systems. Further, there is a need for ink jet compositions that can be selected for a number of imaging processes including those illustrated in U.S. Pat. No. 3,084,043, U.S. Pat. No. 4,794,651, and British Publication 2,169,416 (corresponds to the aforementioned '651 patent), the disclosures of which are totally incorporated herein by reference. An advantage associated with the inks of the present invention resides in the formation of brighter, clearer colors on paper. Another advantage associated with the inks of the present invention in embodiments thereof resides in their thermal stability at temperatures of from about 0.degree. to about 280.degree. C. of the pigments as a result of the silica shell coating of the polymeric cores. Yet another advantage associated with the inks of the present invention in embodiments thereof resides in desirable waterfastness in a range of from about 80 to about 98 percent of the resulting prints as a result of the grafting of the dyes to the polymeric particles. The aforementioned and other advantages are applicable to the ink jet ink compositions of the present invention and the liquid developer compositions illustrated herein in embodiments thereof. Accordingly, while in some instances the present application may refer to ink jet compositions, the reference is substantially equally applicable to liquid developers unless otherwise noted, especially with respect to the objects and advantages achievable with the compositions of the present invention as well as the utilities thereof.